Spinal interlamellar fixation including lumbar sacral fusion and correcting scoliotic curves are well known and frequently used medical procedures. Spinal fixation systems used to correct problems in the lumbar and thoracic portion of the spine, are frequently installed posteriorly on opposite sides of the spinous process and adjacent to the transverse process. Such systems often include spinal instrumentation having connective structures such as a pair of plates and/or rods which are placed on opposite sides of the portion of the spinal column which is intended to be fused.
Pedicle, lateral and oblique mounting means may be used to secure the spinal instrumentation relative to the desired portion of the spine which will be fused by the fixation system. Screws, hooks, clamps and claws have been designed to attach spinal instrumentation to selected vertebrae of the spine. Cross-linking of the spinal instrumentation is designed to prevent migration of the rods or plates and to increase stiffness of the associated medical construct. Even with rigid cross-linking all spinal instrumentation is designed to provide only temporary fixation until solid bone fusion has been completed. Without adequate bone fusion, fatigue endurance of the spinal instrumentation may be exceeded and cause fracture of the rods or plates used with the medical construct.
Various types of pedicle screws, lamina clamps and vertebra hooks or claws have been used to attach spinal rods and spinal plates at desired locations adjacent to a patient's spine. Examples of spinal clamps and hooks are shown in U.S. Pat. Nos. 5,007,909; 5,074,864; 5,102,412; and 5,147,359 for use in fusing selected portions of a patient's spinal column. These patents are incorporated by reference for all purposes within this application. PG,4
Many of the presently available spinal hooks and clamps require assembly of small components while conducting the surgical procedure to attach the hook or clamp to portions of the vertebrae. Presently available spinal fixation systems frequently require careful alignment of the hardware used to connect the components of the spinal instrumentation with each other.
Presently available clamps generally engage the lamina adjacent to a pedicle in only two locations. Vertebra hooks and clamps generally have only one or two points of contact with the lamina. Prior spinal fixation systems which have only one or two points of contact with the lamina tend to move laterally relative to the pedicle and associated vertebra. Since pedicles have a generally elliptical cross section with tapered exterior surfaces, clamping a pedicle is similar to attempting to clamp a cone. Three points of contact are desirable for secure engagement with the selected vertebrae.
A need has thus arisen for improved pedicle clamps to attach spinal instrumentation to selected portion of a patient's spine without requiring additional manipulation of the spinal instrumentation and to minimize the use of pedicle screws while at the same time reducing requirements to assemble small pieces of hardware during the surgical procedure.